How intramolecular hydrogen bonding (IHB) controls the C-ON bond homolysis in alkoxyamines

Recent amazing results (Nkolo et al. , Org. Biomol. Chem. , 2017 , 6167) on the effect of solvents and polarity on the C-ON bond homolysis rate constants k d of alkoxyamine R 1 R 2 NOR 3 led us to re-investigate the antagonistic effect of intramolecular hydrogen-bonding (IHB) on k d . Here, IHB is investigated both in the nitroxyl fragment R 1 R 2 NO and in the alkyl fragment R 3 , as well as between fragments, that is, the donating group on the alkyl fragment and the accepting group on the nitroxyl fragment, and conversely. It appears that IHB between fragments ( inter IHB) strikingly decreases the homolysis rate constant k d , whereas IHB within the fragment ( intra IHB) moderately increases k d . For one alkoxyamine, the simultaneous occurrence of IHB within the nitroxyl fragment and between fragments is reported. The protonation effect is weaker in the presence than in the absence of IHB. A moderate solvent effect is also observed. IHB between alkyl and nitroxyl fragments affords striking changes in k d , affording a nice control of the C-ON bond homolysis.